RFID systems and methods employing infrared localization

ABSTRACT

A series of radio frequency identification (RFID) systems are delineated. One such RFID system comprises an RFID signpost, and a plurality of infrared transmitters, wherein each infrared transmitter of the plurality of infrared transmitters is arranged to cover, when transmitting, a distinct sector relative to the RFID signpost. Another RFID system comprises an RFID signpost having a transmitter for transmitting signals of a predefined type, and a receiver for receiving signals of the predefined type, wherein the transmitter for transmitting signals of the predefined type cannot transmit until a determination is made that the predefined type of signal is not present at the receiver. Still another RFID system comprises an RFID signpost including a transmitter having a continuous power dissipation rating, and a processor for controlling the transmitter such that peak pulse power of a transmission from the transmitter multiplied by its duty cycle does not exceed the continuous power dissipation rating for the transmitter.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from U.S. Appl. No.60/675,280, filed Apr. 26, 2005, in the name of Koerner, et al. andentitled “Radio Frequency Identification Device System with InfraredLocalization,” the full content of which is incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to radio frequency identification (RFID)systems and methods, and more particularly, to RFID systems and methodsemploying infrared (IR) localization.

BACKGROUND OF THE INVENTION

RFID is an automatic identification method, relying on storing andremotely retrieving data using devices called RFID tags, tags ortransponders. An RFID tag is typically a small object that can beattached to or incorporated into an object, animal, or person. RFID tagsmay contain silicon chips and antennas to enable them to receive andrespond to radio-frequency queries from an RFID transceiver. Passivetags require no internal power source, whereas active tags require apower source.

Active tags can periodically transmit their identification (ID) code,status, data and other information for as long as 10 years on a singlebattery. Active tags are capable of communicating with devices, such asa reader, at ranges of several hundred feet. Readers are capable ofnearly simultaneous detection and reading of hundreds or thousands oftags.

In many RFID systems today, there is a need for localization, i.e., theability to accurately determine the location of tagged objects, personsor animals to be within a region of desired dimensions. In a hospitalsetting, for example, it may be useful to know that a particular item ofmedical equipment or a particular person is somewhere within arelatively large area, e.g., 300 feet in any direction from a receiveror a reader. However, it may be useful to know more precisely where aparticular asset, patient or employee is located, and perhaps whetherthe asset, patient or employee is safe and secure. This may be foundfrom the determined location of the asset, patient or employee; thesensor inputs on the related tag or badge; and/or from a local signpost,that might indicate, for example, that a door is not secure, or smokehas been detected.

Similarly, in a mail or package processing center, for example, it maybe useful to know where a specific container is located within afacility, particularly its precise location with respect to key accesspoints, such as the front of a conveyor belt portal or a door. In thisway, the system can more effectively route mail or packages in acontainer to the correct destination. In addition, with improvedlocalization of tracked items down to a particular access point, such asa door, a tag may be turned off (to conserve power) before the relatedcontainer is loaded on its transport and then turned on upon arrival ata specified destination access point.

Some RFID systems employ radio frequency (RF) signals. Radio frequencysignals readily pass through walls, ceilings, floors, etc., however, RFsignals also reflect and refract from various objects in the radiotransmission path. Therefore, attempting to identify tag location basedon RF signal strength has been generally ineffective. Usable RFIDlocalization systems based upon RF signal time-of-flight have beendeveloped and deployed, however, these systems are complex, expensive,and often of limited performance, particularly indoors, because ofreflections and other problems.

Other RFID systems employ IR signals, particularly in an IR signpost,and generally provide relatively better and more precise localization.However, existing RFID systems employing IR signals have limitedlocalization capabilities. There is also a need in existing RFID systemsemploying IR signals to provide system status and other informationthat, in turn, can greatly enhance asset utilization, productivity andsecurity. There is also a need in existing RFID systems employing IRsignals to provide for global interconnection and control of RFIDsystems where overall control and processing capability may be providedremotely, such as via an Internet website. Moreover, existing RFIDsystems employing IR signals generally have rigid hardware designs thatcannot be adapted for use on multiple applications under programmableprocessor and system control.

Thus, a need exists for RFID systems employing IR signals that overcomethese and other problems.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, an RFID systemcomprises an RFID signpost, and a plurality of infrared transmitters,wherein each infrared transmitter of the plurality of infraredtransmitters is arranged to cover, when transmitting, a distinct sectorrelative to the RFID signpost.

In accordance with another embodiment of the invention, an RFID systemcomprises an RFID signpost having a transmitter for transmitting signalsof a predefined type, and a receiver for receiving signals of thepredefined type, wherein the transmitter for transmitting signals of thepredefined type cannot transmit until a determination is made that thepredefined type of signal is not present at the receiver.

In accordance with another embodiment of the invention, an RFID systemcomprises an RFID signpost including a transmitter having a continuouspower dissipation rating, and a processor for controlling thetransmitter such that peak pulse power of a transmission from thetransmitter multiplied by its duty cycle does not exceed the continuouspower dissipation rating for the transmitter.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are exemplary and depict aspects of the disclosedembodiments of the present invention. Accordingly, specific systems orapplications may have numerous signposts, tags, receivers, and/or othersystem components, and may have one local system controller, multiplecontrollers, or operate with or without a network or cable to connect tothe signposts, between signposts and/or a global controller or website.In addition, not all capabilities or functionality must be used in onesystem or application.

FIG. 1 is a block diagram of a plurality of exemplary local controlsystems coupled via the Internet to global or overall processingprovided by a website or a remote global controller and/or processor, inaccordance with systems and methods consistent with the presentinvention.

FIG. 2 is a block diagram of an RFID system including an exemplarysignpost, tag, receiver, system controller, LAN network, and a portableor handheld terminal, in accordance with systems and methods consistentwith the present invention.

FIG. 3 is a block diagram of an exemplary signpost including an AC powersupply or charger, a battery, wired or wireless LAN interface, sensor orcontrol inputs, control outputs, a controller having a processor withmemory, a clock, and an IR transmitter output, in accordance withsystems and methods consistent with the present invention.

FIG. 4 is a block diagram of an exemplary tag including an IR receiver,sensor or control inputs, control outputs, a controller having aprocessor and memory, a battery and a radio transmit output, inaccordance with systems and methods consistent with the presentinvention.

FIG. 5 is an exemplary signpost transmission array including IRtransmitting diodes D1, D2, D3 and D4 that are in a circle around D5, inaccordance with systems and methods consistent with the presentinvention.

FIG. 6 is an exemplary block diagram depicting a non-motion tag strategywith variable beaconing, in accordance with systems and methodsconsistent with the present invention.

DESCRIPTION OF THE EMBODIMENTS

There is a need for improved IR methods of signal generation as well asIR and RF communication formats. Such improved methods and formats may(1) minimize or prevent collisions between signpost or tag signals, (2)enhance data acquisition to include audio, video and image data, (3)improve localization, (4) provide for the capability to operate a systemlocally and/or globally over the Internet, by WI-FI, over telephonelines, cables or other means, (5) determine location or position frommultiple signposts, (6) utilize signposts having multiple transmitteroutputs and signal diversity for improved performance.

One aspect of the present invention may include a monitoring system thatcan operate in an open-loop or one-way fashion, with location, status,data, programs, controls, instructions, or other communication between asignpost to a tag, from the tag to a receiver, and/or from the receiverto a system controller.

Another aspect of the present invention may include a monitoring systemthat can operate in a closed-loop or two-way fashion, with communicationbetween a system controller to a signpost, from the signpost to the tag,from the tag to a receiver, and/or from the receiver to the controller.

Yet another aspect of the present invention may include a monitoringsystem that can interface, communicate and operate with the Internet,and/or remote controllers using WI-FI (Wireless Fidelity), Bluetooth,cellular telephone networks, telephone lines, cables, radio or othermeans, and operate locally, globally or both.

Still another aspect of the present invention may include a monitoringsystem that can communicate and operate with portable terminals, PDAs orcomputers, using IR, RF or other means, or a combination thereof tooperate with a signpost, a tag, a receiver and/or a system controller.

Yet another aspect of the present invention may include a monitoringsystem with a signpost that can transmit an IR signal to a tag, and inaddition, receive inputs from sensors and control devices, provideoutputs to indicators and control devices, and/or provide RF, IR orcable communication with a system controller.

Still another aspect of the present invention may include a monitoringsystem having tags that can receive IR signpost signal inputs; receiveinputs from sensors, such as motion sensors, tamper controls, and otherinputs; provide outputs to controls, indicators, and other devices; andtransmit RF signals to receivers.

Yet another aspect of the present invention may include a monitoringsystem that can determine a tag's location to be within a desired areaor zone, such as a defined location, e.g., in a particular hospital bed,at a particular access point, etc.

Still another aspect of the present invention may include a monitoringsystem that has communication formats with significant data-acquisition,audio and video handling capability, and can receive, control, manageand process tag ID, control, status and/or other significant datareceived from numerous tags and signposts.

Yet another aspect of the present invention may include a monitoringsystem that can receive, encode, store, process and transmit encrypteddata or other coded information, and provide data and control inputs andoutputs to provide security for the system, and other objects, personsor vehicles.

Still another aspect of the present invention may include a monitoringsystem that can provide communication from a signpost to a tag or from atag to a receiver, in a dual-mode asynchronous or synchronous fashion,using special communication formats designed to minimize or preventcollisions with other signposts or tags.

Yet another aspect of the present invention may include a monitoringsystem that can operate with software that determines tag location usingtag signal inputs activated by multiple signposts, and/or from signpoststhat have the ability to locate tags within a portion of a signpostarea, using communication path diversity.

Still another aspect of the present invention may include a monitoringsystem that can operate independently or globally as part of an overallasset or supply-chain control and management system, operating inaccordance with Uniform Code Council (UCC), Electronic Product Code(EPC), International Standards Organization (ISO), InternationalElectrotechnical Commission (IEC), WI-FI or other standards, and/or withoverall system control on a website.

Yet another aspect of the present invention may include using simplifiedand low-cost commodity IR receiver integrated circuits (ICs), devices ormodules in a tag, such as those used to control TVs, tape decks, DVDplayers etc., as well as custom sensor and receiver designs.

Still another aspect of the present invention may include using one ormore IR transmit diodes excited in short pulses to achieve high opticalpower levels to flood a particular room or area with sufficientlydiffuse illumination, so a tag can receive IR data signals in multipleorientations and positions within the room.

Yet another aspect of the present invention may include using high IRtransmit levels such that the optical signal can penetrate portions ofthe human body, such as a hand, and textile and other items, such assheets and blankets, in order to monitor, for example, a patient in abed, and overcome background sun or other light.

Still another aspect of the present invention may include using IR dataencoding having a low number, length, and duty cycle pulse-positionmodulation method or format so that the transmit IR LEDs may be operatedat high-peak current levels, but low-average power levels, in order toachieve strong illumination levels.

Yet another aspect of the present invention may include varying, underprogram control, the amplitude of IR signals in order to vary the range,and to decrease the signal level to reduce the amount of IR diffusion tomake the system operate more line-of-sight, for certain uses andapplications.

Still another aspect of the present invention may include outputting apattern or scanned pattern of IR transmission, such as a rotating IRbeam, and/or varying the IR amplitude and/or receiver directionality orsensitivity, in order to more precisely locate a tag within a definedarea or zone.

Yet another aspect of the present invention may include providingcyclical or synchronous IR signpost data transmission resulting in lowRF transmission density to minimize tag collisions and to minimize oravoid the necessity of expensive tag auxiliary activation devices, suchas a motion sensor.

Still another aspect of the present invention may include providingcyclic sampling of the IR receiver module or device, at low-duty cycles,in order to achieve a fast-reaction time when exposed to new IR signposttransmitters, and to conserve battery power.

Yet another aspect of the present invention may include providing a tagthat can recognize the circumstance of a continued report from the samelocation, and avoid the need for higher current consumption associatedwith a longer or full IR read cycle, except under specifically definedcircumstances.

Still another aspect of the present invention may include providing atag with a memory that can report a current or historical signpostlocation code, as indicated by a status bit transmission, in order toinsure that each valid code is transmitted multiple times, to insuresystem reception when the tag is moving at high speeds.

Yet another aspect of the present invention may include providing an IRsignpost unit that can incorporate an IR sensor that is capable ofdetecting transmissions from a handheld IR terminal or controller, andto stop the IR signpost transmissions to allow the terminal to completeits communication between transmissions.

Still another aspect of the present invention may include providing anIR signpost unit that can incorporate, internally or externally, an IRsensor to detect the activation of a TV or other IR transducer ortransmitter, in order to turn off the system IR transmissions for aperiod, allowing operation of the transducer without interference.

Still another aspect of the present invention may include providingcommunication formats that can be used for data acquisition andtransport, including video or images, with a planned upward path foradding capabilities while maintaining standards, so that system softwarewill not have to change for existing capabilities.

Yet another aspect of the present invention may include using IR, visuallight, laser light, or acoustics, individually, or in some combination,for transmission from a signpost to a tag, as a means of providing abroad and diffused tag localization, or narrower, more focused, discreteor more line-of-sight tag localization, or both.

Still another aspect of the present invention may include providingsmall battery operated signposts that can operate in an array, such asin-line, column and row, star or other pattern, where signpostscommunicate with each other and/or a central controller, using low-powerIR and/or radio means, creating a form of Pico network.

Yet another aspect of the present invention may include providing a tagthat can be located, in a contiguous fashion in single, multiple linearor angular directions, by the use of sum and difference ratio-metricmeans to measure received tag signal levels, or by transmittingdifferent transmit levels with fixed tag thresholds.

Still another aspect of the present invention may include providing atag that, in contrast to some other systems, can transmit the high-ratemanual or alarm initiated transmissions at the same lower or higherpower level as the low-rate self initiated or “beacon” transmission,using the low-density sparse communication format that is employed.

Yet another aspect of the present invention may include providing a tag,that when activated by human intervention, such as when initiated by apanic, motion, emergency, security or other critical input, transmitsinformation at a high rate and at higher power levels than a normalbeacon signal, including sending prior signpost information.

Still another aspect of the present invention may include providing asignpost that can transmit omni-directional IR signals, fan patterns, orother patterns in order to provide targeted location coverage areaswithin a room, such as locating patients in a hospital room and matchingthem with their respective beds.

Yet another aspect of the present invention may include providing asignpost that can transmit or receive IR, RF or acoustics, or two ormore thereof, or a tag that can receive or transmit IR, RF or acousticsor two or more thereof, as a means of providing range information bycomparing the time-of-flight of each signal.

Still another aspect of the present invention may include providing asignpost that can be movable, such as located on a vehicle that canoperate with tags on the vehicle, and/or fixed position tags that canserve as locating and long-range transmission elements for the signpost,thereby reversing the roles of the signpost and tags.

Yet another aspect of the present invention may include providing a tagthat receives a signpost signal, and in order to prevent multiple tagsfrom being synchronized by a signpost and then transmitting at the sametime, transmits a signpost-initiated signal at the next tag-determinedtime that it normally sends a self-initiated transmission.

Still another aspect of the present invention may include providing atag that varies it normal self-initiated or beacon signal at times thatvary based on their identification code, so that even if they transmitat the same time once, in subsequent transmissions, their transmit timeswill vary, thereby preventing signal collisions.

Still another aspect of the present invention may include providing amonitoring and tracking system that is modularized, so that much of theabove-identified functionality and capability can be selectivelyincluded, the system size can be scaled, and it can operate locally orglobally, or both, based on the needs of a specific application.

Reference will now be made in detail to the present exemplaryembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

As shown in FIG. 1, a global control system 10 may include one or morelocal control systems 12, a long-distance or global communication system14, such as the Internet, and a website 16, or other remote or globalcontroller 16. An exemplary embodiment is described using IR and radiowireless communication, as well as signposts that can communicate witheach other and/or the system controller.

Referring to FIG. 2, the local control system (or controller) 12, inoperation with a processor or computer, serves the purpose of receivingtag signals, and for tags 18 within proximity or range of a signpost 20,receives the signpost address or coordinates, status, and associateddata combined with the tag identification (ID), status and associateddata. In this manner, the local control system 12 can determine thepresence of the tags 18 within the larger range of one or more receivers22, and their local location by receipt the signpost address, along withits associated data.

The local controller system 12 can operate over the Internet 14 incommunication with a remote website, global controller or overallmonitoring system 16, which can operate worldwide in concert with one ormany local controller systems 12. A website can process received tag,signpost, sensor and other data and inputs, in accordance with systemsoftware that emulates the system processes and methods, or a portionthereof, normally provided in a local controller 12, or those that maybe performed in a global or overall system controller 16, or both, aswell as provide a central database of inventory, status, itinerary,transactions, and other data.

In a minimum open-loop system configuration or embodiment, employingindependent signposts 20 without the direct bi-directional communicationwith the central controller 12, as shown, the system sends inputs fromthe signpost 20 to the tag 18, then from the tag 18 to one or morereceivers 22, and then to the controller system 12, creating a one-waysystem.

If desired, a pilot, reference, test or check tag can be permanentlymounted internally or in proximity or range of a signpost 20 in order toallow the signpost 20 to communicate with the system controller 12 in amanner that allows signpost sensor or other data transmissions, andtests the signpost, receiver and system controller operation in theabsence of a movable tag 18.

In an enhanced or closed-loop configuration, the signposts 20 areconnected with the central controller 12, as shown, with cable, LANS,Internet, IR, WI-FI, radio or other forms of direct communication, andthe system can send outputs from the signpost 20 to one or more tags 18,then from the tags 18 to one or more receivers 22, and then to thecontroller system 12, and from the controller 12 to the signposts 20,creating a two-way system.

This allows the system controller 12 to send instructions, controls andinput to the signposts 20 and/or tags 18, such as instructions toactivate a signpost output, such as locking a door, sending to a tag 18status or other data updates to change the tags mode of operation, orsending communication synchronization and timing information to asignpost 20 and/or tag 18, in order to minimize or prevent collisions ofsignpost and/or tag signals.

A system controller 12, or a signpost 20, operating independently, canreset or set the time of a tag operation, and in this manner, tags 18 inproximity of a signpost 20, and for some time afterwards, can operate atabsolute times in order to synchronize tag reception and transmission.For example, a tag 18 on a package container or a package in amail-processing center, normally operating asynchronously, upon entry toa travel chokepoint, can be synchronized in time, and its RFtransmission time can be assigned to occur at times that do not collidewith those assigned to other tags 18 or tags 18 activated by othersignposts 20. For containers or people that enter or exit daily orotherwise in a repeatable manner, the time synchronization can then bemaintained over a period or even continuously, being updated often.

More specifically, various aspects of the invention seek to employlow-cost hardware components that are able to achieve fast, nearreal-time, responsiveness as tagged assets and personnel are movingabout within a building or outside. Further, it is desirable toaccomplish this at low current consumption, to preserve long tag orsignpost operating life, using small low-cost commodity batteries or thelike.

A signpost 20, as shown in FIG. 3, may include an AC power supply or acharger 24, a battery 26, wired or wireless LAN interface 28, sensor orcontrol inputs 30, control outputs 32, a controller 34 having aprocessor with memory, a clock 36, and an IR transmitter output 38.

The primary purpose of the signpost 20 is to locate the tag 18 to alocal area, or to a portion of the local area, in a very economical andsimple fashion. This may be done by sending, using IR transmission,identification, status, sensor, control, programming and other data andassociated information, within a local area from the signpost 20 to atag 18 or multiple tags 18. In turn, the tag 18 operates in accordancewith preset or received control instructions, to transmit ahigh-frequency radio output with selected identification, data, controland status information, along with received local signpost information,to a long-range high-frequency RF or radio receiver 22.

As an example, a signpost 20 is located in manner to transmit to a tag18 at a slow beacon rate its identification, verifying the signpostpresence and nearby location. The tag 18 is tracked by a receiver 22within distances of hundreds of feet, however, when the tag 18 movesthrough a designated doorway or key access point, the tag 18 comes intoclose proximity of a signpost 20 that, in turn, causes the tag 18 totransmit at a higher rate both its own identification and informationpertaining to the specific signpost 20. The reception of the tag RFsignal by a receiver 22 or receivers 22, with local locationinformation, then tells the system controller 12 and/or the associatedcomputer system 15 where the tag 18 is within a proximity area, or aportion of the proximity area.

Signposts 20 are generally inexpensive, but provide valuablelocalization information by their signpost identification, and caninstruct the tag 18 to perform multiple functions including turn on,turn off, operate at a low, medium or high rate, operate for a specificperiod of time and then turn off, synchronize the tag operation, oroperate in any other mode. In this manner, the tag 18 can operate atvery low power rates or can be completely off until information isneeded, such as when passing through a door or other salient location.

Signposts 20 can operate on AC power 24 or on battery power 26, or both.Signposts 20 can operate completely independently or while communicatingto a remote controller 12 system by wire, LAN, WI-FI, Internet, powerline carrier, radio, IR or other means, and have the capability,although not necessarily all in one system, to handle the followingexemplary access control, security, and environmental inputs andoutputs.

Access control inputs may include inputs such as proximity, metal,weight, drive over, door, gate, light, IR, handle, access code, card,key, or tag, eye pattern, fingerprint, voice and/or video camera,sensors, readers or detectors, and outputs to operate items such asdoors, gates, signs, lights, and/or indicators. Security inputs mayinclude inputs such as hazardous material, radiation, drug, and tampersensors, readers or detectors, and outputs, such as alarms, warninglights, displays, restraints and/or remote notification. Environmentalinputs may include inputs such as temperature, water, light, power,moisture, voltage and pressure sensors, readers and detectors, andoutputs, such as heaters, coolers, motors, pumps, fans, and/or lights.

In addition, time inputs or internal time and date-keeping capabilitymay be maintained independently or synchronized or set by systemcontroller 12, clock or by radio synchronized time input, in order tomaintain access control or other functions that vary with time, such aswhen a facility is closed, for security and other purposes, or atime-and-date stamp for sending to a tag 18 for recording and/or radiocommunication.

In a system having direct communication between each signposts 20, orthe signposts 20 and the system controller 12, or those having aself-contained time generator that is synchronized by time broadcasts,common resets or other means, the system can prevent collision betweensignpost IR transmissions by time-division multiplexing with eachsignpost 20 transmitting at different times in a cyclical fashion wherea first signpost transmits at time T1, a second signpost transmit attime T2 etc., or the transmissions can be interleaved in a manner basedon a priority method, however, the cyclical operation can also beaugmented by having a priority system where one signpost 20 caninterrupt or override other signpost transmissions.

If the control system 12 detects a critical condition, such as a tag orsignpost signal indicating a security breach, or it detects hazardousmaterial, the system 12 can assign the appropriate signpost 20 a highertransmission priority, and, for example, send instructions to thesignpost 20, or all signposts 20, to stop access and raise an alarm. Thesystem 12 can also receive or request a video or image of the signpostarea, for security or a record of events.

In a system not having direct communication between each signpost 20, orthe signposts 20 and the system controller 12, and does not have aself-contained time generator or time base, there may be situations,such as when signposts 20 are in separate rooms, where collisions of thesignpost signals will not occur.

However, whether such collisions might or might not occur, a specialpulse low-duty cycle method of asynchronous pulse communication may beused where an IR signpost signal and a radio tag signal can overlap, andcontinue to operate, with an occasional collision that can be detectedand accounted for, and, if necessary, rejected, as disclosed in U.S.Pat. No. 6,611,556, which is incorporated herein by reference.

Alternatively or in addition to the pulse method of transmission, andwithout having absolute time base, an algorithm can program the signpostsignal times to vary in a predetermined fashion so that each signpost 20will eventually have a period where no other signpost 20 istransmitting.

A signpost 20, with a proximity sensor or detector, if activated, maysend its signal to a tag 18 at an increased rate, and in a configurationhaving connection with the local control system 12, may contain, forexample, a door access control output, that results in a item or personhaving access or entry only if they have an appropriate tag or badge, asdetermined by the local control system 12.

As such, the system addresses a low-cost IR augmentation mechanism forRFID beacon tags, which provides reliable local area, zone, chokepointor room-by-room tag localization. Each room or portal region underlocalization may be fitted with one or more low-cost IR signposttransmitter units that can continuously beacon a location or addresscode. The signpost address or coordinates do not identify the signpost,but identify where the signpost is located. In this way, if the signpostis replaced in the same location, the transmitted address code remainsthe same. The address code can be programmed in the field to define itslocation or coordinates.

An exemplary signpost transmit array is shown in FIG. 5. The arraycomprises a simplified example embodiment of an array of four transmitdiodes (D1-D4) in a circle located 90-degrees apart from each other, andone (D5) in the center. Higher positional resolution can be achievedwith more diodes, such as 8 diodes, each located 45 degrees apart fromeach other, or even more diodes. Each of the outer diodes (D1-D4) may begenerally pointed in a direction away from where diode (D5) is located,so when activated in time sequence, they (D1-D4) create a scanningpattern of IR radiation similar to a flash light pointing and rotatingin directions of 0, 90, 180 and 270 degrees. If mounted on a ceiling,the diodes (D1-D5) may all face down and the diodes in the outer circle(D1-D4) may face down angularly towards the floor, to point towards tags18. It also may be desirable to use lens and/or shielding, to obtain thedesired width and relative spacing of the IR radiation patterns.

The purpose of this configuration, instead of using just one centerdiode (D5) that radiates IR omni-directionally, is to provide theability to locate a tag 18 within a portion or a segment of theproximity area of the signpost 20, and is understood best by explainingits operation. A proximity area of a signpost is the entire area inwhich a signpost IR transmission is readily detectable by a tag.

The signpost 20 first outputs an omni-directional output by activatingdiode D5, and transmitting the signpost ID and other associatedinformation, including control data that indicates that a sequentialmultiple read-cycle will follow. This wakes up the tag 18 andsynchronizes it (or many tags 18) for reading additional data thatfollows, where diode D5 is turned off and diode D1 is activated followedin a time sequence by D2, D3 and D4. The tag 18 knows what the activateddiode is by its time of transmission and arrival. Alternatively, thesignal transmission of each diode can result in a code indicating itsspecific identity, operation or direction.

In the example shown, the tag 18 is located in the upper right corner ofFIG. 5 and receives the input from diode D5 since it radiatesomni-directionally. Since the tag 18 is closest in angle to D2 itreceives the most intense signal from D2, and less signal from D1, andlittle or no signal from D3 and D4, as they are pointing in the oppositedirection of tag 18. In a most simple system, the tag 18, as it is movedaround, would “see” only the IR outer ring diodes shining directlytowards it.

However, if the tag 18 was equipped with an IR receiver with asignal-strength-indicator (SSI), the tag 18 could “see” each diode(D1-D4) as it was the read in time sequence, the relative diode signalstrength indicating tag localization. If the tag 18 was located directlybetween two diodes, the tag 18 would receive approximately equal, butreduced outputs from the two diodes, indicating that the tag 18 wascentered between the diodes. As the tag 18 is moved in an angularposition around the center of the array, one of the closest diodeamplitudes goes down, as another goes up, indicating that the tag ismoving toward the later and away from the former.

If the outer diodes (D1-D4) are read by the tag 18 ratio-metrically, thedifference of their received amplitudes divided by their sums, centeringa tag 18 between two diodes will create a zero output, and when the tag18 is moved in one direction the ratio is positive and goes up inamplitude, and when moved in the other direction, is negative and goesdown in amplitude. It can be seen that the angular position of the tag18 can be resolved to a much higher resolution than indicated by thenumber of diodes, however, as a practical matter, the use of SSI makesthe tag circuitry more complex, as it is generally not a feature oflow-cost TV-type IR receiver chips or modules.

However, many other practical issues also make it difficult for such asimple system to operate effectively. For example, if the outer ringdiodes (D1-D4) are transmitting at very high levels, sufficient IR maybounce or reflect around the room and cause false reads, the angular IRoutput of the diodes may overlap or be insufficient to cover the entire360 degree range, and if the tag 18 is moved directly under the diodes,the ability to resolve angular position will decrease the closer the tag18 gets to the diodes (D1-D4).

Therefore, a practical system generally needs more diodes, generally 8or more in the outer circle, to provide an overlap of coverage, and toprovide adequate determination of the angular location to a reasonableresolution. The diode transmission amplitudes need to be sufficient toreach or be in range of the tag 18, but not be in excess, and it may benecessary to put multiple diode arrays in a room. For example, fourdiode arrays can be put into a room, with one in each corner, and thediodes that point towards the walls can be made inactive, blocked orremoved. The four diode arrays can be operated with one master signpost20 and a number of slave signposts 20, or one signpost 20 can drive anumber of remote diode arrays

In this case, the position of the tag 18 can be better determined fromthe four arrays, particularly when the tag 18 is moved through the room,as it should always be in range of one of the four arrays, and if in thecenter of the room, read approximately equally by all four arrays. Inaddition, instead of using SSI in the tag 18 to measure the signalstrength, a tag 18 having a fixed level of signal sensitivity can beused, in conjunction with signpost transmit signals that can be variedin amplitude.

The same sequence of reading the outer diodes, D1, D2, D3 and D4 may beused, however, multiple read cycles may be sent with each read cyclehaving a different amplitude. This may be accomplished, in an exemplaryembodiment, by having a programmable current source drive an array ofdiodes, so that the diode current levels are programmed as the diodesare activated in time sequence, or by the use of different diodes havingdifferent output levels. In this manner, the read cycles having only onediode read will be the diode closest to the tag 18. By having a profileof reads at different amplitudes, one can determine roughly where thetag 18 is between two-array diodes.

For example, assume that the array of diodes (D1-D4) are sequentiallystepped through eight amplitude levels, highest (level 1) to lowest(level 8). Assume at level 5, diodes D1, D2 and D3 are detected andread, then at the next lower level amplitude level of 6, only diodes D1and D2 are read, and then at level 7, only diode D2 is read. Thissequence indicates that the tag 18 is closest in direction to diode, 2and closer to diode 1 than to diode 3. It can be seen that as few as twodiodes can be used to determine position on either side of a chokepoint, such as a door, and it can be determined what direction the tag18 is going through the door.

It should be understood and appreciated that the pattern of diodes mayvary substantially. For example, instead of a whole circle of diodes,only diodes representing two directions or a reduced angle of directionmay be used or activated. In addition, instead of IR, visual light froma diode or laser may be used, with tags 18 having receivers sensitive tovisual or laser light, or the signpost 20 and tags 18 may use, incombination, visual light, laser light and IR, or some othercombination. This has the advantage that IR can be used to broadly floodan area to activate tags 18 that are not in direct line-of-sight withthe signpost diodes, and visual or laser light can be used to locate thetags 18 within an area with more of a directed, targeted orline-if-sight operation, for increased position resolution.

A tag 18, as shown in FIG. 4, may include an IR receiver 40, sensor orcontrol inputs 42, such as a motion sensor, control outputs 44, such asa light indicator, a controller 46 having a processor and memory, abattery 48, and a radio transmit output 50. An exemplary tag embodimentmay use RF for the radio transmit output, although the transmit outputcould also be IR, acoustic, or a combination thereof.

Tags 18 within proximity or range of the IR signpost transmitter 38detect the infrared signal, and relay the location code along with itsown tag ID code and associated data to RFID receivers units 22, whichare local or more centrally and widely distributed within a desiredarea. The RFID receivers units 22 are, in turn, networked andinterconnected with one or more system controllers 12 and one or morehost computers 15. In an indoor application, the infrared signal doesnot penetrate walls, ceilings and flooring, so an effective localizationcapability is achieved without overlap or interference.

The tag output signal does not have to be analyzed for positioning sincethe tag output signal is the mechanism for communicating the signpostlocalization information. If operating at a typical 300 to 900 MHz, agreat deal of overlap can be provided to insure reception, however, thesignal reception is not in itself needed to be used for local or finepositioning. This is a significant issue when the problems of signalreflections and other issues of operating in a complex environment areunderstood.

Tags 18 can employ encrypted IR data input, and or RF output, in orderto prevent tampering or access of secure tag data or information. Thiscan be accomplished by the local system controller 12, or a globalcontroller, using a key to encrypt and to create unencrypted data sentto or received from a signpost 20 or tag 18. However, the encoding ofsignals to transmit them and the decoding of signals to receive themshould not to be confused with encryption for security purposes.

Tag capabilities, in summary, may include dual antenna outputs fordiversity of antenna patterns for improved range and constancy ofperformance; extended battery life because of lower beacon duty cyclesthat speed up with signpost input; extended battery life with lowerbeacon duty cycles that speed up with motion detection, general locatingcapability as determined by which receivers 22 are receiving tagsignals; local position input from a signpost 20 that is thentransmitted to a receiver 22; tag beacon operation and/or signpostinstituted transmission, or both; encoded bits for collision management;sensor inputs, such as motion detector, tamper switch, moisture, tilt,radiation detectors etc.; control outputs, such as a visual or acousticindicator; dual modes of operation with asynchronous and synchronousoperation; IR receiver signal sampling to reduce tag current; and pulsecommunication for high peak RF communication signals levels.

Having such accurate real-time asset and personnel localizationinformation can greatly enhance productivity and asset utilization.

Regarding the issue of signpost high power IR illumination, in typicalconsumer TV channel-changer applications, the IR diode is driven atapproximately 20 milliamps. That amount of drive current provides asatisfactory operation when the IR LED is aimed directly at the receivermodule. In the tag locating problem, in general, one may not have theluxury of direct alignment of the transmitting IR LED (withapproximately a 20° beam width) and the IR receiver module (withapproximately a 30° beam width). It is practical, however, to make asignpost IR transmitter, which is enormously brighter and therebycapable of activating the tag's IR receiver module, even when the IRbeam should traverse multiple diffuse reflections from wall, ceiling,floor, furniture etc.

Such a high-powered IR transmitter has been constructed for experiments.The design utilized four banks of 3 LEDs (i.e. 3, 6, 9, or 12 LEDs canbe active for testing). Since the IR LEDs may be used at low duty cycle,they can be powered at high current levels; a test circuit can beoperated to drive the LEDs with 650 milliamps for 3, 6, 9, or 12 LEDs.Consequently, the IR illumination using 12 LEDs is roughly 350 timesgreater than a typical television channel-changer. This is actuallyquite practical using a conventional wall power outlet, because thecircuitry is simple and the components are inexpensive. The IR LEDs thatwere used (the Everlight IR 204-A LEDs) cost only six cents each.

The proto-type signpost 20 may be powered by a lead-acid battery tofacilitate untethered experimentation in different positions andlocations. It was used in conjunction with a portable IR receiver moduletest circuit, which was powered by a 3 V lithium battery (simulating atag 18). The signpost 20 was controlled by an MSP430-microcontroller(available from Texas Instruments) programmed to issue a blink ofsimulated IR location data every second. The signpost 20 transmittedomnidirectionally with 12 LEDs in the LED bank. At the receiver,detection of the IR data blink was indicated by a visible light LED.

The resulting coverage performance with the high-powered transmitter wasquite satisfactory. The tag receiver was noted to respond to the IRbursts in any position and orientation of the tag receiver unit or anyorientation of the IR transmitter. Satisfactory operation was observedwhen the simulated tag 18 was placed deep in a shelf or backed tightlyagainst a wall or even under a table. Satisfactory operation was alsoobserved through multiple layers of textile and through portions of thehuman body, such as the hand or forearm.

A simple and effective strategy was found to be to direct the IR LEDstowards the ceiling providing diffuse illumination throughout the room,although any aiming direction was acceptable. This was effective insmaller rooms or in a large room of 20′ by 40′ dimensions. The onlycircumstance which precluded IR coupling was when the tag receiver wasplaced in a substantially light tight container, a closed cupboard or aclosed drawer.

Regarding the tag IR receiver, for simplicity and lower cost, the tag IRreceiver can utilize existing consumer electronic components for IRsignaling to television sets, stereo receivers, DVD decks, etc. Thesetypes of products typically employ an integrated IR receiver module thatcomprises sensitive detection electronics, as well as an IR receiverdiode in one component package.

The associated electronics perform several functions: they detectmodulated in-band IR by means of a bandpass filter; they provideautomatic gain control and level adaptation, as well as low-level signaldetection. This type of functionality is desirable for operation over asignificant distance, particularly when there is lighting and other IRsources in the environment. These modules have evolved in design overmany years and are made in large volumes and at low cost.

Manufacturers in the IR receiver module business include SharpElectronics and Vishay Semiconductor, though tag 18 may utilize anyconventional IR receiver module. In some respects, such IR receivermodules may not be ideally suited for application in RFID tags 18. Mostof these product offerings are intended for 5 V operation and will notwork on a 3 V battery. The majority are also leaded components which addboard space and assembly cost to a small RFID tag 18. Most also consumeseveral milliamps of current.

So far, the preferred IR receiver module appears to be a Sharp offeringin a leaded package, sold under part no. GP1UW700QS, which operates downto 2.4 V at 500 microamperes. Although 500 microamperes is low, comparedto the majority of available receiver modules, it is still large for atag having a typical average current budget of 2 microamps. Thus, thereceiver module should be powered only for brief periods on a low dutycycle.

It may be possible to design a custom IR receiver chip, which would bemore optimally suited to this problem. Such a custom IR receiver chipwould optimally provide a smaller circuit board footprint, loweroperating voltage and ultralow current consumption.

Experimentation was also conducted with direct sunlight shining on thetag IR receiver module. In this circumstance, the tag IR receiver moduleworked less effectively. It was observed that when sunlight falls withinthe main beam of the IR receiver module, there is no operation. Whensunlight is off axis, operation occurs only when the IR transmitter isrelatively close to the IR receiver module. Operation will thereforelikely be predominantly limited to indoor or covered applications. Forexample, truck loading dock application scenario could be contemplated,only if it were substantially shrouded from direct sun. Alternatively, atruck loading dock application could be well served by a portablesignpost transmitter, which is temporarily placed within the body of thetruck thus using the truck itself as a shroud for sunlight.

Regarding the issue of waveform design and tag battery life, constraintsinherent to the tag's IR receiver module impact battery life. Similarly,message waveform duration impacts battery life.

Experiments suggest that the IR receiver module should be powered-up forat least 2 ms prior to receiving IR signals, in order to detect signalbursts with full sensitivity. In some cases, detection will occur within1 ms of power up, but with reduced sensitivity. The battery chargeconsumption for a minimal power up interval is 2 ms×500 uA=1 uC. Incomparison, the battery consumption associated with a single RFbeaconing event with an RF Code tag is approximately 3 uC for a US tagversion (RF Code tag no. 05102050-52 was used). Thus, when an IR readattempt occurs immediately preceding each beacon event and no IR signalis detected, the additional consumption imposed on the battery is 33%,which can be reasonably tolerated.

However, if an IR signal is present during a 2 ms sample period and thetag 18 proceeds to read the IR signal data, then the tag 18 would needto extend the receiver module on-time to first complete the message inprogress, then detect a fresh start pulse and a complete identificationmessage from the transmitter. So, on average, the on-time for the tag'sIR receiver module would need to be 2 ms, plus 150% of a single completetransmission.

The proposed message duration may be calculated as follows. Experimentalobservations have shown that approximately 11 IR modulation pulses aredesired, per burst, for good pulse sensitivity at the tag's IR receivermodule. Using 36 kHz modulation, an eleven pulse burst takes 305.55 μs.Conversely, 10 cycles of the watch crystal frequency, 32.768 kHz, takes305.18 μs. Thus, 11 cycles of modulation is numerically convenient sincedata clocking from a 36.000 kHz signpost crystal will agree to within0.12% with the tag sampling process, which is clocked using a low-costcommodity 32.768 kHz crystal.

In order to operate the signpost's IR LEDs, such as the one or more LEDsthat may represent diode D5 in FIG. 5 at high-pulse current, the LEDduty cycle should be proportionately reduced from their nominal 100 mAcontinuous current specification. However, a code employing high-dutycycle is necessarily spread in time, which has negative implicationswith respect to IR collisions and a negative impact on tag batteryconsumption during a read cycle. An additional factor favoring operationat low duty cycle is that the tag's IR receiver module adaptationfunction performs better—lower duty cycle will give better sensitivity.

A desirable solution is to use two-bit pulse position modulation codingfor the IR transmission signals from the signpost 20. By that strategy,exactly 1 pulse will be transmitted in each successive group of fourtimes slots. This results in an allowable pulse current of 400 mA—nearlyas aggressive as the 650 mA used in the experimental signpost simulator.Thus, the time interval required per bit is 2×11=22 modulation periods.

For IR transmission signals from the signpost 20, a message comprising11 bits of message value, five bits of preamble and eight bits ofchecksum—24 bits—may be used. In addition, there should be a message gapand a start bit; that can be approximated as 2 additional bits or 26total. So, the overall time duration of the contemplated message is26×22=572 modulation, periods. Employing 36 kHz modulation, thatcomputes to about 16 ms.

So the average required on-time for the tag's IR receiver module is 2ms, plus 150% of 16 ms=26 ms to receive an IR location message withchecksum and header. The battery cost is therefore 26 ms×500 uA=13 uC.

For the purpose of battery life analysis, it is sensible to consider thecase of several baseline tag configurations wherein the tag 18 spendsits entire life in the presence of an IR signpost 20. For the baselineconfiguration, it is presumed that a single IR read occurs prior toevery RF beacon occurrence. The table below provides a comparison ofbattery life for an MSP430 microcontroller-based US tag with and withoutbaseline IR signpost functionality and based on the waveform parametershere contemplated. For simplicity, this table does not incorporate abattery end-of-life performance factor or self-discharge model. Thetable is based upon a linear battery life of 22 microampere-years(CR2032, a battery part no. available from Maxell Corp.) and presumes aforward diode drop on MSP430 Vdd pin for 1.0 μA continuous consumptionby the microcontroller.

Battery Life Calculation (Years)

(1 Battery/2 Batteries) RF only Tag (not being Signpost Tag activated by(activated by a a signpost) signpost) 30 sec beacon 20/40 15/30 10 secbeacon 17/34  9/18  3 sec beacon 11/22 4/8  1 sec beacon 5.5/11  1.6/3.230 sec background + 15% motion at 1 sec 14/28  6/12 30 sec background +15% motion at .5 sec 11/22 4/8

The IR read process has an impact on battery life, especially whenshorter beacon intervals are required for better response time behavior.A technique is also disclosed which can significantly reduce currentconsumption while still providing fast IR reaction times. A benefit ofthis scheme is that the relatively expensive motion sensor component intag 18 can be eliminated. There is presumed to be a need for a taglocating function when a person or asset quickly traverses a definedregion of space inside a building. Thus, the duration of exposure to theIR signpost may be short.

One can assume that successive IR signpost portals can be spaced apartso that surrounding the portal there is a region with no IRtransmission. This installation constraint may be required for reliablefast reaction at “portals.” For room to room locating performance, thereis no similar need for significant separation. In general, room to roomlocating capability and portal capability would not need to be locatedtogether.

Referring to FIG. 6, one can consider a non-motion tag strategy withvariable beaconing. The tag 18 may employ regular IR sampling at a onesecond interval, while no signpost signal is present or at a two secondinterval when a signpost signal is present. At each sample time, the tag18 turns on its IR receiver for 2 ms looking for an IR signpost signal.If a signpost signal is not present, the tag 18 increments a counter. Ifthat counter is less than a predefined limit, e.g., 20, the tag 18 goesback to sleep. At the 20th successive occurrence of no signal, an RFbeacon report will be transmitted. At a sampling occasion, when a newsignpost signal is first detected (i.e. when no signal was detected onthe previous sample), the tag 18 initiates an IR read cycle andimmediately generates an RF transmission including the new signpostlocation code. Conversely, when there is continuing successive signpostsignals, the tag 18 increments a continuation counter. If thecontinuation count is less than a predefined limit, e.g., 10, the tag 18goes back to sleep on a two-second cycle. Otherwise, on the 10thsuccessive signpost detection, the tag 18 initiates an IR read cycle andan RF beacon cycle in succession. Under continuous signpost signaldetection, the beacon cycle occurs every 20 seconds.

The net effect is that the tag 18 is responsive to a new signpost signalwithin one second as long as there was at least a single precedingsample with no signpost signal present. If a signpost signal iscontinuously absent or continuously present, the tag 18 reports on a20-second beacon cycle.

Using the waveform assumptions, as before, one can calculate expectedbattery life for this strategy, as depicted in FIG. 6. The table belowindicates battery life for a 20-second background beacon and for a60-second background beacon. The table indicates battery life where asignpost signal is continuously present and where signpost signal iscontinuously absent.

Battery Life Using Variable Beaconing Strategy (Years)

(1 Battery/2 Batteries) Signpost Signpost Absent Present 60 secbackground beacon; 1 sec IR 10.7/21  12.5/25   response 20 secbackground beacon; 1 sec IR 10/20 10/20 response

The table above demonstrates that this arrangement results insubstantially balanced battery consumption, whether the signpost signalis present or not. Ten-year battery life is achieved using a single cellin each case (albeit without accounting for battery dating orself-discharge).

Besides eliminating the need for an expensive motion sensor in the tag18, the variable beaconing strategy has another advantage. Compared to amotion-sensor-based strategy, this technique greatly reduces the tagreporting density when assets are in motion. As a result, the potentialfor transient circumstances of very high pulse density and unmanageableRF collisions is substantially eliminated.

Another advantage to this approach is that it facilitates rapidcommunications startup with an IR programming fixture. An IR programmingfixture will issue an IR attention signal for one second, followed bythe programming messages as may be required. Because the tag 18 samplesevery second (with no signal present), one is assured that the tag 18will catch the attention signal and the subsequent messages at the firstinstance of transmission. To accomplish fast startup by a motion-sensorstrategy, tags 18 would need to be shaken while programming. This wouldbe awkward and less reliable.

Typically, a tag 18 will always transmit its last known signpostlocation report. Even after the tag 18 leaves the field of the signpost20, the tag 18 will continue to transmit the last known signpostposition. A single bit in a tag message format may be used to indicatewhether the signpost report is current or historical. This feature willassure that brief portal passages are reported at multiple beacontransmissions, so as to resolve the possibility of data loss due to RFcollision occurrence.

Regarding the issue of compatibility with IR remote control devices,since the IR signpost 20 will typically operate at illumination levelsgenerally greater than typical IR remote control units, there is a needfor an anti-collision mechanism, so that the IR signpost 20 does notprevent operation of handheld remote controls. Even though handheldremote controls are usually operated by pointing the device directly atthe receiving unit, that direct illumination may still not be sufficientto overcome the general diffuse illumination from the a signpost 20located in the same room.

The signpost IR transmissions are pulse position waveforms which operateat a duty cycle such that there are substantial off periods punctuatedby pulse bursts of IR illumination. The signpost 20 will itself befitted with one or more sensitive IR receivers. These receivers may beset for detection of the common pulse modulation frequencies that areassociated with various consumer products, including television sets,stereo receivers, DVD decks and the like. This includes frequency use of36 kHz, 38 kHz, 40 kHz, as well as some other frequencies that are lesscommonly used, if desired. The output state of these IR receivers willbe monitored between every pulse burst of the IR signpost 20. At thefirst instant that signal is detected on one of these modulationchannels, the IR signpost 20 will instantly cease operation for adesired interval, e.g., around five seconds. This quiet interval willallow the handheld remote control to complete its messaging to theconsumer product of interest. In general, the waveform associated withthese consumer products includes a significant start pulse intervaland/or a repeating message which is transmitted two or three times.Thus, even though a collision is possible for the duration of onesignpost pulse burst, while the signpost's IR receiver modules areblinded, that very brief initial collision will be of no import.

There is a practical and more general alternative to the use of separatereceiver modules for every modulation frequency of interest (orconcern). It is possible to employ digital signal processing technologyto simultaneously detect multiple modulation frequencies from a singlesensor. By this approach, a single photo diode could be utilized with ananalog-to-digital converter, which is continuously sampling theillumination level at a regular frequency that is at least as great astwo times the highest modulation frequency of interest. The output ofthe converter would feed a microcontroller or DSP chip, whereappropriate algorithms may reside for detection of IR transmissions.Such algorithms are well known.

To facilitate reliable detection of the IR signal from a low-powerhandheld controller it is generally preferred to locate the signpost 20in close proximity to the consumer product targeted by the controller.In this way, the IR signal which is pointed towards the consumer productand intended to activate it will also simultaneously activate the IRdetector in the signpost 20.

It is possible that practical considerations regarding defining the IRcoverage area of the signpost 20 in the room may dictate a mountinglocation for the signpost 20, which is not optimally close to theconsumer product of interest. To accommodate that circumstance, a relayunit having a remote sensor may be utilized. The remote sensor may becoupled to the signpost 20 by dedicated wiring, power line signaling,radio link or an optical link, for example.

The use of such a remote sensor module may also be dictated under thecircumstance of a room having multiple consumer products which arecontrolled by an IR controller and which are located at differentpositions in the room. In this circumstance, it may not be possible tolocate a signpost 20 in close proximity to all of the consumer products.

Regarding the issue of system expansion, in order to a make the systemexpandable, with added functions and capabilities, it is desirable tohave communication formats that can vary to meet a wide range ofapplications and are expandable as required. Stated simply,communication formats need to be as simple and short as possible, butneed to be able to grow to add new capabilities and functions, even ifall the future possibilities are not presently known.

This objective may be accomplished with formats that, for a particularapplication, allow you to pick and choose among existing features andfunctions, and yet be able to add new ones that are not presentlydefined. A first element in accomplishing this is to have a highlydisciplined, comprehensive and planned communication format that has thebuilt-in flexibility to change or expand. A second element is tomaintain the standards over time, for example, if the status of the tagbattery voltage is determined by an eight-bit data format, then the samestandard should be used for all tags 18 for this purpose in allapplications. A third element is to have a format that makes sure thatthe exemplary eight-bit data format that is the same in allapplications, is defined or called out in the same fashion in allapplications.

In these ways, the system software does not have to change when readingthe same data for the same function or feature in all applications, asit can be programmed to match the selected variable of the tags 18 andother hardware. If the format is considered a key, then the same key maybe used in the hardware and software so that everything works together.If something new is added then hardware may need to have expandedcapability or be programmed to handle a new sensor or other variable. Anew corresponding software module may need to be added to read and usethe data. However, if one is going to read temperature on two tags 18 intwo applications, using the same sensor, then the data format shouldremain the same, and the corresponding software module should remain thesame.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A radio frequency identification (RFID) system, comprising: an RFIDsignpost; and a plurality of infrared transmitters; wherein eachinfrared transmitter of the plurality of infrared transmitters isarranged to cover, when transmitting, a distinct sector relative to theRFID signpost.
 2. The RFID system of claim 1 further including one ormore RFID tags.
 3. The RFID system of claim 2 wherein each of the one ormore RFID tags includes an infrared receiver.
 4. The RFID system ofclaim 1 further including one or more additional RFID signposts, each ofthe one or more additional RFID signposts having a plurality of infraredtransmitters wherein each infrared transmitter of the plurality ofinfrared transmitters is arranged to cover, when transmitting, adistinct sector relative to a respective one of the one or moreadditional RFID signposts.
 5. The RFID system of claim 2 wherein eachinfrared transmitter of the plurality of infrared transmitters altersthe amplitude of signal transmission in a predefined manner to enable adetermination to be made as to the position of the one or more RFID tagsrelative to the RFID signpost.
 6. The RFID system of claim 5 wherein thepredefined manner comprises one of increasing or decreasing theamplitude of signal transmission sequentially.
 7. A radio frequencyidentification (RFID) system, comprising: an RFID signpost having atransmitter for transmitting signals of a predefined type; and areceiver for receiving signals of the predefined type; wherein thetransmitter for transmitting signals of the predefined type cannottransmit until a determination is made that the predefined type ofsignal is not present at the receiver.
 8. The RFID system of claim 7wherein the predefined type of signal comprises one an infrared signal,an acoustic signal, a visible light signal and a radio signal.
 9. TheRFID system of claim 7 wherein the signal of the predefined type is usedto control a device that is not part of the RFID system.
 10. A radiofrequency identification (RFID) system, comprising: an RFID signpostincluding a transmitter having a continuous power dissipation rating;and a processor for controlling the transmitter such that peak pulsepower of a transmission from the transmitter multiplied by its dutycycle does not exceed the continuous power dissipation rating for thetransmitter.
 11. The RFID system of claim 10 wherein the processorcontrols the transmitter such that peak pulse power of the transmissionfrom the transmitter multiplied by its duty cycle does not fall below apredefined limit.
 12. The RFID system of claim 10 wherein thetransmitter comprises one or more infrared light emitting diodes.